The present invention is directed to novel indium-based shape memory alloys, and especially to novel indium-thallium shape memory alloys. The invention is also directed to an electrolytic process for the production of shape memory alloys.
Certain indium-based alloys are known to exhibit a shape memory effect whereby an article constructed of the alloy "remembers" a certain configuration and assumes that configuration when it is within a certain temperature range. Shape memory alloys are characterized by a parent (beta) phase at a higher first temperature and a martensitic phase or structure at a lower second temperature.
An article of a shape memory alloy in the parent phase can be changed to a martensitic structure by bringing the article below a critical temperature or otherwise applying sufficient stress thereto. The article is then deformed into a second shape. The article of the second shape is then heated to a temperature above the critical temperature, the martensitic structure becomes unstable and the alloy reverts to the parent phase. As the alloy structure reverts to the parent phase, the article regains its first shape, that is, the shape the article had initially when it was in the parent phase, prior to quenching and deformation.
Certain alloys comprising indium and thallium have been recognized as exhibiting shape memory effect. Rogen, U.S. Pat. No. 3,999,790, discloses a heat releasable lock which may be constructed of indium-thallium-nickel-aluminide shape memory alloy. Rogen, U.S. Pat. No. 4,018,547, discloses an oil well pump which may comprise an indium-thallium shape memory component. Chiang et al., U.S. Pat. Nos. 4,732,556, 4,738,610 and 4,797,085, disclose an apparatus comprising a shape memory alloy die which may be constructed of indium-thallium.
Indium-thallium alloys may be produced by thermal methods or by electrolytic methods. Although each alloy production technique has its own advantages which may be specifically desirable for certain applications, electrolytic techniques are suitable for high volume manufacture, provide ease of process control, can be used for thin film applications including microelectronics, and require a relatively low amount of investment in equipment and set up.
In applications where it is desirable to have shape memory alloy material on remote interior surfaces, it may be difficult or impossible to locate thermally prepared shape memory alloy material at these sites. By electrodeposition, it is possible to deposit thin films of material onto such remote interior surfaces of substrates. Additionally, electrolytic methods are generally more suitable than thermal techniques for the production of alloys in thin cross section.